Can I define new attributes in XMP for PDF?

Question

I know there are some attributes in XMP for PDF files such as:

     <xap:ModifyDate>2009-12-10T09:54:47-05:00</xap:ModifyDate>
     <xap:CreateDate>2009-12-10T09:42:54-05:00</xap:CreateDate>
     <xap:MetadataDate>2009-12-10T09:54:47-05:00</xap:MetadataDate>
     <xap:CreatorTool>Adobe InDesign CS4 (6.0.4)</xap:CreatorTool>

But I want to define custom attributes for example:

     <xap:ViewTitle>2009-12-10T09:54:47-05:00</xap:ViewTitle>
     <xap:GUID>2009-12-10T09:42:54-05:00</xap:GUID>

Can I do it?

Answer 1

Yes, you can.

According to XMP Specification

New properties may be added to existing namespaces without “breaking” applications.

The definitions of properties in existing namespaces should always remain the same; otherwise, applications may produce incorrect behavior. If it is necessary to change the meaning of a property, a new property should be created (and the old one declared as deprecated).

And you can create new custom schemas. Probably it's a better approach than extending existing schema.

More information can be found in Extensibility of Schemas in XMP Specification.

Answer 2

You can use the XMP bridge libraryto edit XMP. Marijan Tompa gave great insights on its blog : http://indisnip.wordpress.com/2010/09/07/storing-custom-data-into-indesign-file-xmp/